Tissue fusion or coagulation by an electrode that introduces current locally into tissue and/or tissue fluid is known from, for example, EP 1 862 137 A1. In the course of treatment, effects arise in tissue in the vicinity of the electrode that lead to a change in tissue impedance. At the start of the effect, the tissue has an initial impedance that is reduced to a lower value shortly after current starts to flow, designated as “phase I”. After a period of time, the tissue impedance rises again, designated as “phase II”. The tissue impedance in Phase II generally reaches values that lie markedly above the initial impedance. The rise in impedance then flattens out and may reach a stable end value, referred to as “phase III”.
The length in time of phases I and II and the slope of the fall and rise in impedance determine the quality of the surgical result attained.
The system according to EP 1 862 137 A1 therefore attempts to bring the change in tissue impedance over time into line with a target curve. For this purpose, the system continuously compares the actual tissue impedance value measured in a suitable manner to the target value that applies for the particular point in time. If a deviation is found, then a counter-measure is implemented (for example, an increase or decrease in the energy introduced into the tissue). The control technology approach that forms the basis for this technique, however, can reach its limits if control deviations that have led to an irreversible change in tissue structure (e.g., a premature protein denaturation) have occurred.
A robust and reliable method for the performance of tissue fusion or coagulation, in particular long-term sealing of vessels, is therefore desired. A device that enables this method is also similarly sought.